In a micromechanical sensor and/or a method for manufacturing a micromechanical sensor for detecting a state variable of a substance, the sensor includes at least one heating element, one temperature measuring element and optionally an inlet opening into and/or an outlet opening out of the cavity for this purpose. The sensor includes a cavity configured to at least partially receive the substance through one of the inlet openings and discharge it again at least partially through one of the outlets or outlet openings. The at least one state variable of the substance is detected here as a function of at least one variable representing the operation of the at least one heating element and/or the operation of the at least one temperature element.